Security systems are presently limited in their ability to detect contraband, weapons, explosives, and other dangerous objects concealed under clothing. Metal detectors and chemical sniffers are commonly used for the detection of large metal objects and certain types of explosives; however, there exists a wide range of dangerous objects that cannot be detected using these devices. Plastic and ceramic weapons increase the types of non-metallic objects that security personnel are required to detect. Manual searching of subjects is slow, inconvenient, and generally not well-tolerated by the public, especially as a standard procedure in high traffic centers, such as airports.
It is well-known to those of ordinary skill in the art that images of objects comprising various types of materials can be generated using X-ray scattering. The intensity of scattered X-rays is related to the atomic number of the material scattering the X-rays. In general, for atomic numbers less then 25, the intensity of X-ray backscatter, or X-ray reflectance, decreases as the atomic number increases.
Objects are potentially visible in X-ray images of persons due to the difference in X-ray reflectance between the objects and human tissue. Non-metallic objects are commonly composed of low atomic number elements similar to those of human tissue, i.e. hydrogen, carbon, nitrogen, and oxygen. Soft human tissue scatters a significant amount of X-rays due to the relatively low atomic number of hydrogen, carbon, and oxygen in relatively high concentration. Due to the high atomic number of calcium, bones near the surface of the body, comprised mainly of calcium, produce much less scatter. Concealed objects, especially metals, can be easily visualized in the images due to their significant difference in atomic composition from the background of human tissue.
Further, objects having similar atomic composition as the human body tend to present contours and edges when hidden underneath clothing or on the surface of the subject's body. Particularly, X-ray scattering is reduced around contours and edges due to the contours and edges absorbing scatter on one side of the edge and increasing scatter on the other side of the edge.
In conventional systems, especially of the X-ray transmission type, an operator is required to identify very low contrast objects in the presence of image clutter resulting from the imaging of internal human anatomy. The difficulty of this task results in poor detection capability for a wide range of dangerous objects composed of low atomic number elements, such as plastics or ceramics, which are often masked by the low atomic number elements which comprise the human body.
Edge detection effects or contour effects may be used for automatically and uniformly enhancing the image edges of low atomic number concealed objects to facilitate their detection. Edge enhancement is provided while simultaneously suppressing the edges of internal anatomy that produce confusion in image interpretation.
Radiant energy imaging systems for detecting concealed objects have been disclosed in the prior art. For example, U.S. Pat. No. RE28544, assigned to AS&E, Inc, discloses “a radiant energy imaging apparatus, comprising: a source of a pencil beam of X-ray radiant energy; radiant energy detecting means defining a curve in fixed relationship to said source; means for scanning with said pencil beam said radiant energy detecting means along said curve to provide an image signal representative of the radiant energy response of the medium in a region traversed by said pencil beam along a path to said detecting means; means for relatively displacing said region and an assembly comprising said source and said detecting means to establish relative translating motion in a direction transverse to a line joining said source and said detecting means to produce a sequence of image signals representative of the radiant energy response of said region in two dimensions; and means responsive to said image signals for producing an image representative of said response.” The X-ray potential, however, is set at up to 150 Kilovolts and is specifically chosen to transmit X-rays through the person being examined. Operation of the X-ray tube at 150 Kilovolts or even at 100 Kilovolts would negate benefits of imaging by backscatter detection, e.g., low dose scanning. This technique requires the subject to be exposed to a substantial radiation dosage, especially if the subject is scanned often, e.g., a frequent airport traveler.
U.S. Pat. No. 4,839,913, also assigned to AS&E, Inc, describes “an apparatus useful in imaging for inspecting objects to highlight targeted components of selected radiation signature comprising: (a) a source of penetrating radiation selected to object, (b) means for repeatedly scanning a pencil beam of radiation, from said source along a line in space, (c) means providing relative motion between said object to be imaged and said line in space, (d) first radiation energy detector means located to be responsive to radiant energy penetrating said object and emerging from said object, substantially unchanged in direction, for producing first electrical signals, (e) second radiant energy detector means responsive to a predetermined fluorescent radiation line emitted from said targeted components of said object for generating second electrical signals, (f) display means responsive to said first electrical signals for producing a shadowgraph image of said object, and (g) first means responsive to said second electrical signals for generating an indication of presence of said predetermined fluorescent radiation line.” The energy level of the source, however, must be sufficient to excite a selected fluorescence radiation line so that the fluorescent radiation line has sufficient energy to escape the object. Thus, it may be necessary to expose the object to relatively high X-ray energy in order to detect certain materials, which would be unacceptable for personnel inspection systems.
In addition, U.S. Pat. No. 4,799,247, also assigned to AS&E, Inc., discloses “a projection imaging system for inspecting objects for highlighting low Z materials comprising: (a) a source of penetrating radiation, (b) means for forming radiation emitted by said source into a beam of predetermined cross-section and for repeatedly sweeping said beam across a line in space, (c) means for moving said object to be imaged relative to said source in a direction perpendicular to said line in space, (d) first radiant energy detector means located to be responsive to radiant energy penetrating said object and emerging from said object, substantially unchanged in direction, for producing first electrical signals, (e) second radiant energy detector means located further from said source than said object and responsive to radiant energy scattered by said object for producing second electrical signals, (f) third radiant energy detector means located closer to said source than said object and responsive to radiant energy scattered by said object for producing third electrical signals, (g) display means responsive to at least a pair of said electrical signals for separately, independently and simultaneously displaying said pair of electrical signals as a function of time.” With the incident beam being of sufficient energy to provide both transmitted and backscattered signals, the X-ray energy must be relatively high, similar to that of the patents described above, making such a system undesirable for personnel inspection.
U.S. Pat. No. 6,965,340, assigned to Agilent Technologies, discloses “a security inspection system, comprising: a portal through which a human subject is capable of walking; a scanning panel including an array of antenna elements, each of said antenna elements being programmable with a respective phase delay to direct a beam of microwave illumination toward a target on the human subject, said antenna elements being further capable of receiving reflected microwave illumination reflected from the target; and a processor operable to measure an intensity of the reflected microwave illumination to determine a value of a pixel within an image of the human subject constructed by said processor”.
U.S. Pat. No. 5,181,234, assigned to Rapiscan Security Products, discloses an X-ray imaging apparatus for detecting a low atomic number object carried by or on a human body positioned at a distance from said apparatus comprising: x-ray source for producing a pencil beam of X-rays directed toward said human body; scanning means for moving the region of intersection of said pencil beam and said human body over the surface of said human body in a scanning cycle, said scanning cycle being sufficiently short to expose said human body to a low radiation dose; a detector assembly providing a signal representative of the intensity of the X-rays scattered from said human body as a result of being scanned by said scanning means, said detector assembly being disposed on a same side of said human body as said X-ray source and having an active area with dimensions sufficient to receive a substantial portion of said scattered X-rays to provide a coefficient of variation of less than 10 percent in said signal; and display means to presenting characteristics of the detector signal to an operator; wherein said scattered X-rays are distributed across said detector to create an edge effect which enhances edges of said low atomic number object to enable detection. The contents of this patent are herein incorporated by reference in their entirety.
U.S. Pat. No. 6,094,472, also assigned to Rapiscan Security Products, describes an X-ray imaging apparatus for detecting an object carried by or on a body moving relative to the apparatus, said apparatus having an entrance and an exit, said apparatus comprising: a passageway extending at least from said entrance to said exit; at least one X-ray source having means for producing a pencil beam of X-rays directed toward said body in said passageway, said pencil beam intersecting said body at a region of intersection corresponding to a pixel having a pixel value; a scanning means disposed adjacent said at least one X-ray source for moving the region of intersection of said pencil beam and said body over a surface of said body; a tracking means for causing the scanning means to substantially track said body as it moves with respect to said apparatus from said entrance to said exit; a detector assembly for detecting an intensity of X-rays scattered from said body as a result of being scanned by said first scanning means and for generating a signal representative of the intensity of the scattered X-rays, said detector assembly comprising a plurality of detectors; and display means for presenting characteristics of the detector signal to an operator.
U.S. Pat. No. 6,967,612, assigned to Gorman, John D. et al, discloses “a system for standoff detection of human carried explosives (HCE) within an area under surveillance, comprising: an active radar system, the radar system having a radar transmitter, a radar receiver, at least one radar antenna, and a field of regard; a radar tracking control system in physical cooperation with the active radar system, wherein the field of regard of the active radar system is targeted within the area under surveillance, the area of surveillance being greater than the radar field of regard; a user interface having a video display terminal and a data input means; a computer in electrical communication with the radar system, the radar tracking control system, and the user interface, the computer having a central processing unit, a memory and computer readable program code stored in the memory, the code including: radar tracking instruction means for targeting the radar system; and HCE detection instruction means for detection of human carried explosive devices.”
The abovementioned conventional systems have substantial disadvantages, however. In existing systems, detailed images are produced by characteristics of the subject's body and any object concealed under the subject's clothing. The system operator then inspects each image for evidence of concealed objects. The system operator and security personnel responsible for analyzing conventional images are thus privy to these personal anatomical details.
In addition, communication between the system operator and security personnel is often hindered due to airport noise, lack of privacy, and the presence of large amounts of people and/or equipment between the image analyst and the system operator.
Further, the communication of the exact location of a perceived threat can be confusing. For example, when indicating whether a threat is on the left or right of a subject's body, it is often difficult to communicate a common frame of reference. Thus, in order to avoid confusion or miscommunication, the image analyst and system operator often spend several minutes communicating the perceived location of the threat, which is often unreliable. In addition, the perceived location of the threat may be initially misdirected, requiring security personnel to perform a full pat-down anyway to discover the actual location of the threat, and if such threat is present.
Thus, even in instances where a physical search or “pat-down” is required on a specified portion of the body of the subject, security personnel generally perform a full body pat-down. A full body pat-down, however, is often time-consuming and uncomfortable for both the security personnel and the subject under inspection. The time consumed performing full-body pat-downs further decreases throughput, thus making the process slow and inconvenient for other subjects who are in queue for security screening.
Thus, the prior art does not provide a system that achieves the correct balance between the conflicting, yet equally important principles of maximizing security and inspection capability while retaining a sufficient level of comfort and privacy for the person under inspection by directing the “pat-down” to a specific location.
In the light of the abovementioned disadvantages, there is a need for an X-ray inspection system that allows for maximum threat detection performance with an improved communication between an image analyst and the system operator, thus allowing for a directed physical search and minimal “pat-down” of subjects under inspection.
In addition, there is a need for an X-ray inspection system that allows for higher throughput owing to enhanced verbal and visual communication between system operator and image analyst and ease of use. In addition, what is needed is a people screening system that has higher throughput, resulting in higher security and overall lower cost of operation.